Thermal sprayed coatings are influenced by the wettabillity of the molten particles to substrates. The contact angles of several molten metal droplets are measured in air and vacuum. The flattening ratio is evaluated by taking into account of wettability. Comparing with the experimental data of the freefall droplet, it was concluded that the wettability to the roughened substrates influenced on the flattening characteristics.

The quality of thermal sprayed coatings greatly depends on the individual flattened splats. Generally they are characterized by two main factors, flattening ratio and splat profile. The flattening ratio is specified straightforward, but it is difficult what factor should be selected from the various properties for the splat profiles. Fractal geometry is introduced to the profile evaluation of the splats which are formed by the free-fall metal droplets and by the alumina coatings using plasma spraying method. The fractal dimension of each splat was measured by SIA (Slit Island Analysis) technique which measures the ratio of area to contour length of the island appeared on the horizontally sliced plane of the splat. The obtained fractal dimension was related to with Re and We numbers in a bi-linear form, which is the same characteristics as the unevenness ratio obtained previously. It was concluded that fractal dimension is an effective measure to evaluate the splat profile.

Adhesion of ceramic coatings considerably depends on the surface characteristics of blasted substrates. The roughened surfaces have two kinds of topographical characteristics, one is of their cross section and the other is of planar. The roughened surfaces is generated by angled grit-blasting process which can be expected to improve the adhesion of ceramic coatings. The topography of the roughened surfaces has fractal characteristics in their cross section and has been more effectively related to the adhesive strength of ceramic coatings than average surface roughness traditionally used. This paper presents that fractal characteristics is evaluated in the planar topography of the blasted surfaces and shows that the planar fractal characteristics is closely related adhesion of ceramic coatings. The planar fractal dimension is evaluated by SIA (Slit Island Analysis) which needs the height data on the roughened surface. Those data are obtained by a laser-microscope in confocal type.